The present invention relates to electrically operated valves and particularly to valves operated by a solenoid for proportional control of flow through the valve in response to an electrical signal. It has been desired to provide such a valve for controlling refrigerant flow in vehicle passenger compartment air conditioning systems such that electronic control of the refrigerant flow to the evaporator may be provided to permit faster response to changing thermal load conditions and improved temperature control of the passenger compartment.
Heretofore, it has been common practice in automotive passenger compartment air conditioning systems to employ a mechanical expansion valve for controlling refrigerant flow to the evaporator which is operated by a temperature sensitive capsule filled with fluid where expansion and contraction of the fluid with temperature changes causes movement of the valve member for controlling flow to the evaporator. Mechanical thermal expansion valves of the aforesaid type have proven to be low in manufacturing cost and reliable for extended periods of service as encountered in automotive applications. However, the mechanical thermal expansion valve has the disadvantage that it can only react to changes in temperature of the fluid in the capsule which is typically thermally connected to the refrigerant discharging from the evaporator. Thus, The thermal expansion valve cannot anticipate changes in thermal load on the system and control refrigerant flow to accommodate the rapid changes. Thus, it has been desired to provide an electrically operated expansion valve for use in automotive air conditioning systems.
However, in designing an electrically operated valve for use as a refrigerant expansion valve and in particular for automotive air conditioning applications, it has been found difficult to provide such a valve which is low in manufacturing cost and rugged and reliable enough for automotive service applications. In such applications, it has been found desirable to utilize a solenoid as the electrical operator for the refrigerant valve inasmuch as a solenoid can provide armature movement proportional to variations in a control signal applied to the solenoid coil and thus can provide a proportional control electrically operated refrigerant expansion valve.
In providing an electrically operated proportional filter control valve employed as a refrigerant expansion valve, it has been found necessary to utilize thermistor temperature sensing elements in sensing ports formed in the valve block in order to provide the necessary temperature inputs to the electrical control system generating the control signal for the valve solenoid. Typically, the thermistor sensing probes are inserted in sensing ports provided in the side of the valve block; and, the solenoid coil is mounted on the end of the valve block for actuating the valve controlling armature. Thus, separate electrical connections are required for the coil and for the thermistors in order to connect the valve in circuit with an electronic controller.
Thus it has been desired to provide an electrically operated valve suitable for controlling refrigerant expansion and particularly in automotive air conditioning applications which provides thermistor temperature probes in valve sensing ports and also provides for electrical connection to a solenoid for electrical proportional control of the valve operator. It has been particularly desired to provide such a valve which is low in manufacturing cost and easily assembled in high volume mass production particularly in the quantities required for automotive vehicle production applications.